LOS ANGELES, California (CNN) -- Questions swirled Friday about the possible role prescription medications may have played in the death Thursday of pop idol Michael Jackson, people close to him said.

The cause of pop star Michael Jackson's death has not been determined after Friday's autopsy.

His autopsy was completed, but further tests must be carried out before the cause of death can be determined, a spokesman for the Los Angeles County Coroner said.

Craig Harvey said the tests would take four to six weeks, after which "we anticipate being able to close the case and issuing a final cause of death." Among the tests to be carried out, he said, are neuropathology (brain) and pulmonary (lung) tests.

Harvey added, "We know that he was taking some prescription medications," but said he was not able to divulge what.

In 2005, after he was cleared on charges of child molestation, Jackson spent a week at a center run by Dr. Deepak Chopra, a physician who focuses on spirituality and the mind-body connection.

During that week, Jackson asked Chopra for a prescription for a narcotic, the doctor told CNN. "I said, 'What the heck do you want a narcotic prescription for?' And it suddenly dawned on me that he was probably taking these and that he had probably a number of doctors who were giving him these prescriptions, so I confronted him with that. At first, he denied it. Then, he said he was in a lot of pain."

Don't Miss

"For a while, I lost him," he said. "I have had that happen with me with other celebrities in Hollywood. There's a plethora of doctors in Hollywood, they're drug peddlers, they're drug pushers, they just happen to be having a medical license and I hope that this episode today, this tragic death of a great human being, will bring to light the huge problem we have in Hollywood with some of the medical establishment, the celebrity doctors, who not only initiate people into the drug experience, but then they perpetuate it so that people become dependent on them."

Chopra said Jackson had recently gone on a diet to prepare for his planned comeback tour, which was to have begun next month in England, and was excited about his planned resumption of his performing career.

"He was practicing, he was fasting, and yet he wasn't physically in the condition to do this, and he was not confronting his drug addiction, which is the big problem," Chopra said.

He blamed Jackson's death on drug abuse, though he offered no direct evidence. "When you have enough drugs in your system, your heart goes into an arrhythmia and your respiration stops," he said. "I think the drugs killed him."

Chopra said he had known Jackson to take the opium-derived painkiller OxyContin at one time, as well as injections of the narcotic pain reliever Demerol "and other narcotics, and I was really desperate to try to help him, but you know you can't help somebody who would go into denial." Watch crowds gather at the hospital. »

Jackson typically would refuse to call Chopra for several weeks at a time, the doctor said. "Then he would call me two or three weeks later and say he was sorry, that he had been busy and it wasn't the drugs -- but it was the drugs."

Chopra, who said he knew Jackson for more than two decades, described him as "my little brother -- I feel very bad for him."

Brian Oxman, a former attorney for the Jackson family who was with the family in the hospital emergency room on Thursday, also expressed concern about medications the pop star was taking.

"I talked to his family about it, I warned them -- I said that Michael is overmedicating and that I did not want to see this kind of a case develop," Oxman told CNN's "American Morning" on Friday.

He referred to Anna Nicole Smith, the former model and reality TV show star who died of an overdose in 2007.

Oxman emphasized that he did not know what killed Jackson, and was not making accusations against any individual.

Jackson's ex-wife, Lisa Marie Presley, said in an online blog posted Friday that she was not surprised by Thursday's news.

She said she divorced him in January 1996, after less than two years of marriage, because she was "in over my head in trying" to save Jackson "from the inevitable, which is what has just happened."

Jackson talked with her about his death during "a deep conversation" 14 years ago about "the circumstances of my father's death," she wrote, referring to Elvis Presley. The singer collapsed in the bathroom of his Memphis, Tennessee, mansion -- Graceland -- on August 16, 1977, at the age of 42. While his death was ruled the result of an irregular heartbeat, the autopsy report was sealed amid accusations that abuse of prescription drugs caused the problem.

The similarity to the "King of Rock" apparently resonated with the "King of Pop." "At some point he paused, he stared at me very intensely and he stated with an almost calm certainty, 'I am afraid that I am going to end up like him, the way he did,' " Presley said. Watch crowds gather at the hospital. »

"I promptly tried to deter him from the idea, at which point he just shrugged his shoulders and nodded almost matter of fact as if to let me know, he knew what he knew and that was kind of that."

That conversation haunted Presley as she watched television coverage of Jackson's death Thursday, she said.

"I am sitting here watching on the news [as] an ambulance leaves the driveway of his home, the big gates, the crowds outside the gates, the coverage, the crowds outside the hospital, the cause of death and what may have led up to it and the memory of this conversation hit me, as did the unstoppable tears," she wrote.

"A predicted ending by him, by loved ones and by me, but what I didn't predict was how much it was going to hurt when it finally happened."

Meanwhile, police -- who had spoken Thursday with Dr. Conrad Murray, who was with Jackson when he died -- were trying to reach him again Friday.

A car that Murray had parked at Jackson's home was impounded and may contain medications pertinent to the investigation, said Detective Agustin Villanueva of the Los Angeles Police Department.

Public records show the impounded car was registered to a Texas woman who is an associate of the cardiologist, who is licensed in California and Texas and also has an office in Las Vegas, Nevada.

CNN's calls to Murray's office were not returned Friday.

AEG Live, the promoter of Jackson's planned tour, said their deal with the singer included a dedicated private physician of his choosing and that Jackson chose Murray, his physician of three years.

A source close to the family said Murray spent much of the last two months with Jackson, as he prepared for his upcoming concert series. The doctor is said to be cooperating with officials.

Jackson was in cardiac arrest when paramedics took him Thursday from his home to Ronald Reagan UCLA Medical Center, where the music idol was pronounced dead at 2:26 p.m. (5:26 p.m. ET). Listen to the 911 call »

He had been preparing for a comeback tour -- aimed at extending his legendary career and helping him to pay off hundreds of millions of dollars in debt.

Jackson began his professional work at age 5, singing with his brothers, before shooting to superstardom as a solo singer. He had numerous No. 1 hits -- the best known being "Thriller," the best-selling album of all time, at an estimated 50 million copies worldwide.

After dominating the popular music scene for years, Jackson became reclusive and mired in scandals that included child molestation charges. He reached a settlement with one accuser and was acquitted in another case after a highly publicized trial in Santa Maria, California, in June 2005.

Jackson is survived by his three children, Prince Michael I, Paris and Prince Michael II.

Condolences and appreciations continued to pour in Thursday from around the world. President Obama said he considered Jackson a "spectacular performer" and expressed his condolences to the Jackson family, the White House said Friday.

At a briefing with reporters, White House spokesman Robert Gibbs said he spoke with the president Friday morning about the death of the pop superstar.

"He said to me that, obviously, Michael Jackson was a spectacular performer, a music icon. I think everybody remembers hearing his songs, watching him moonwalk on television during Motown's 25th anniversary."

But Gibbs said the president also noted that "aspects of his life were sad and tragic. His condolences went out to the Jackson family and to fans that mourned his loss."

In a written statement, Jackson's second ex-wife, Debbie Rowe Jackson, said, "Though Michael is now at peace, the world has lost a beautiful and loving soul. I appreciate the outpouring of support and prayer for Michael, all of his family, me and our children, and hope our privacy can be respected at this difficult time."